(a) Field of the Invention
The present invention relates to audio systems and more particularly to an analog circuit design of combination equalizer and calibrator circuit assembly for audio system that allows pre-calibration of an audio system.
(b) Description of the Prior Art
An equalizer or tone control is commonly used in an audio system to correct, or equalize, the frequency response of a signal. As shown in FIG. 1, when an audio player, such as a CD player, a DVD player, or an AM/FM radio tuner or any other sound source outputs an audio signal to the input end of an equalizer, the frequency and amplitude of the audio signal are adjusted by the equalizer, then the signal outputted is sent to a volume control circuit, then the signal is amplified by an audio amplifier to drive a speaker for audio output. At this time, a user may manually adjust the amplitude of each predetermined frequency without regard to acoustic balance. Regular audio systems may have adjusting means for high frequency control, middle frequency control, low frequency control, tone control, or graphic equalizer tone control, however they do not allow calibration. A user may calibrate an audio system manually according to one's personal preferences. This calibration method cannot achieve balanced frequency and amplitude responses. On regular audio reproduction devices, more particularly, speakers, it is difficult to obtain a balanced frequency response. Especially at low frequency band, a standing wave may remain in a constant position in a space corresponding to a specific frequency, causing variations in sound strength, i.e., formation of wave peak and wave valley in the space. This variation results in an amplitude distortion. It causes an uncomfortable hearing event. This problem exists in regular audio systems, and is difficult to eliminate.
A method is known to have independent devices such as signal generator, spectrum analyzer, test microphone, graphic equalizer, audio amplifier, speaker system, etc., be used together for testing and calibrating an audio system. However, these test systems are expensive systems. The operation of these test systems requires a special technique. Only professional technicians can use these systems. Therefore, these test systems are commonly used for testing space responses such as in concert hall, opera theater, or on stage for considerations in correction of the curvature of the wall, modification of upholstery materials, or installation of acoustic diffusers or acoustic absorbing materials to reduce standing waves and improve the effect for listening. However, these professional test devices are expensive and require much installation space, not affordable by an ordinary user.
It is well known that an audio system must be well calibrated to provide an accurate sound effect. However, the equalizer and tone control of a regular audio system are simply provided for adjustment subject to the user's preference. Therefore, it is desirable to provide an audio system that eliminates the aforesaid problems and achieves perfect reproduction of the original sound.